JPS63280960A - Piston ring made of steel - Google Patents

Abstract

PURPOSE:To prevent any damage caused by partial embrittlement after nitriding treatment in corner part of a piston ring nitriding treatment, a ring by performing chamfer of a dimension within a specific range on the corner part, the piston ring made of steel used for a internal combustion engine, after nitriding treatment. CONSTITUTION:Chamfering is applied within a range from 0.15-0.60mm at the cross-sectional corner part of a piston ring made of steel on which nitriding treatment is made by a depth of 100-200mum. And the steel contains C 3.0-0.9%, Si less than 2.0%, Mu less than 2.0% and Cr 2.0-9.0.% by wt. And, as a constitutional element of steel, Al shoule be contained in the component mentioned 0.3-2.0%. Al is contained to improve the nitriding property. Furthermore, one kind or more than two kinds of W, Mo, V and Nb can also be contained. It chamfering by at least, 0.15mm is applied on the corner part, the nitrided layer 9 can be obtained in an uniform depth, and resultantly, concentration of stress is alleviated and embrittlement can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a steel piston ring that is nitrided and used in an internal combustion engine.

[Conventional technology]

As the performance of internal combustion engines has improved in recent years, there has been a demand for lighter internal combustion engines, and by reducing the axial width of piston rings, it is possible to reduce the weight of not only the piston rings themselves but also the entire engine. As a result of the active promotion of weight reduction, due to recent strength problems,
Steel piston rings are now being used instead of the traditional cast iron piston rings. However, even if steel piston rings are used as the base material, their wear resistance will be insufficient, so at least some kind of surface treatment such as nitriding should be applied to the outer circumferential surface, either alone or in combination. are doing.

[Problem that the invention seeks to solve]

As the performance of automobiles and other vehicles improves, the depth of surface nitriding treatment has been increased from 20 to 20 mm in order to improve the wear resistance of piston rings.
From about 40 μm, it has become deeper to 100 to 200 μm. However, if the nitriding depth is 100~
Piston rings with a thickness of about 200 μm sometimes break at the corners of the piston rings during assembly to the piston or during operation of an internal combustion engine.

As a means to solve such problems, Japanese Patent Application Laid-Open No. 1986-15
The one disclosed in No. 2668 is known. This was done in consideration of the cause of breakage, which is the occurrence of cracks in the nitrided layer on the inner circumferential surface of the piston ring.After the inner circumferential surface of the steel piston ring is prevented from nitriding, the remaining surface is nitrided.

Based on the above facts, the present inventors further investigated this breakage phenomenon in detail. As a result, when deep nitriding treatment of 100 to 200 μm was performed, the corner portion was damaged by the upper surface 2 or 2 of the piston ring, as shown in FIG. Since nitriding progresses simultaneously from both sides of the lower surface 3 and the inner circumferential surface 4 or outer circumferential surface 5, the nitrided layer 7 at the corner portion has a deeper nitrided depth than other nitrided layer portions 8 and has a higher nitrogen concentration. It was confirmed that some parts had become brittle. That is, the present inventors have found that the cause of breakage is due to fatigue fracture caused by partial embrittlement of the corner portion and stress concentration at the corner portion.

By the way, piston rings are damaged during engine operation.
Since it slides with the cylinder, there are problems with wear and seizure with the cylinder, so materials with high wear resistance and seizure resistance are required. When an engine is in operation, the piston moves in a complicated manner within the groove in which it is installed, so fatigue strength and high toughness are required. As engines become faster, these required characteristics are becoming higher and higher. Also,
Ring processability into piston rings is also required.

In view of these circumstances, the present invention has developed a steel piston ring that prevents breakage from the corners and has the various characteristics required for piston rings, such as wear resistance, seizure resistance, and ring processability. This is what we are trying to provide.

[Means for solving problems]

The present invention provides a nitrided steel piston ring having a depth of 100 to 200 μm, in which the steel contains 0.3 to 0.9% by weight of C, 2.0% or less of Si, and 2.0% of Mn.
The steel contains Cr of 0% or less and 2.0 to 9.0% of Cr, and has a Cr content of 0.0% or less and a Cr content of 2.0 to 9.0%.
This is a steel piston ring characterized by chamfering in the range of 15-0.60 m.

In order to solve the above-mentioned problems, the inventors conducted a detailed study on the relationship between corner shape and breakage resistance, and as a result, as shown in Fig.
By chamfering ya (dimensions a and b in the figure), a nitrided layer 9 with a uniform depth can be obtained, reducing stress concentration, and the nitrogen concentration at the corners will not become high, so embrittlement will not occur. On the other hand, for piston rings used in this type of application,
Practically speaking, the upper limit of corner chamfering is 0.6 nm due to the design constraints of its original functions of airtightness and seizure resistance. In addition, Fig. 2 is a graph showing the relationship between corner chamfer dimensions and fatigue strength, and one chamfer dimension is 0.6.
It can be seen that even if it exceeds +m, the effect of improving fatigue strength is saturated.

For the above reasons, the corner chamfer size was set to 0.15.
-0.60no.

Although FIG. 1 shows an R-shaped chamfer, the chamfer shape of the steel piston ring of the present invention is not limited to this. For example, even if the shape is as shown in Figures 3 to 5, the chamfer size a on the upper or lower side of the corner and the chamfer size on the inner or outer side are 0.15-0.60+n.
It is sufficient if the chamfer size is within this range, and the effects of the present invention can be obtained as long as the chamfer size is within this range.

Furthermore, as a secondary effect, slight damage caused to the corners during the manufacture of the piston ring's flat wire material causes rapid deterioration of breakage resistance, similar to the embrittlement of the corners due to nitriding. By implementing the present invention, the breakage rate was reduced and the yield was improved.

Next, the chemical components of the steel piston ring of the present invention will be explained.

C is an element that dissolves in solid solution in iron and contributes to strength, and is an important element that forms carbides and contributes to wear resistance, so it is required to be at least 0.3%.

However, like N, C is an interstitial solid solution element in iron, so adding a large amount inhibits the diffusion of nitrogen during nitriding, making it impossible to obtain a sufficient nitrided layer, and also preventing processing during ring forming. Since it also harms sex, the upper limit was set at 0.9%.

SL is an element added as a deoxidizing agent during the production of steel ingots, and in addition to being a deoxidizing agent, it has the effect of increasing the elastic limit as an alloying element. Addition exceeding this range lowers cold workability, so this was set as the upper limit.

Like Si, Mn is an element added as a deoxidizing agent during the production of steel ingots, and if it exceeds 21 parts, it impairs hot workability, so this was set as the upper limit.

Cr is an additive-forming element and is important for imparting wear resistance. It is also an element that increases the hardness of the nitrided layer. In particular, since it has a high affinity with nitrogen and forms a hard nitride, it is an essential element for materials to be nitrided to a thickness of 100 to 200 μm as in the present invention. In order to fully obtain these effects, it is necessary to add at least 2.0% or more. However, adding a large amount not only forms a lot of carbides, reduces the toughness of the material, and deteriorates ring processability, but also makes it difficult to obtain a sufficient nitriding depth in the nitriding layer. The upper limit was set.

Further, in the present invention, the above components may contain 0.3 to 2.0% of A1.

A1 is included to improve nitriding properties, but if it is less than 0.3%, a sufficient effect cannot be obtained;
%, oxide-based inclusions increase significantly and fatigue strength decreases. Therefore, it is set at 0.3 to 2.0%.

Furthermore, one or more of W, Mo, (1) and Nb may be contained. All of these elements increase tempering softening resistance and high temperature strength, and V and Nb in particular form hard nitrides through nitriding treatment,
It also has the effect of improving surface hardness. However, 2.5
If it is added in excess of %, it increases the amount of hard carbides and causes a decrease in fatigue strength, and is an expensive element.
If it is included, it should be limited to 2.5% or less.

〔Example〕

The present invention will be explained below based on examples.

After melting and casting martensitic stainless steel having the chemical composition shown in Table 1 in an electric furnace to form an ingot,
A billet was formed by blooming, and this was hot rolled into a 5.5φ coil. After drawing this coil, it is cold rolled into a second
Surface chamfer dimensions (B = 2.5 mm, T = 3, 6 m
In order to process the coil into a coil having the following characteristics (Fig. 6), the coil was tempered to HRC42 by quenching and annealing, and then nitrided to a depth of 200 μm from the surface (held at 540°C for 30 hours using a gas nitriding method). , was used as the test material.

Table 1: Chemical composition (wt%) Table 2: The chamfered shape of this sample material is rounded as shown in FIG. 6, so R=a=b.

Using the above test materials, breakage resistance was evaluated in terms of fatigue strength. Figure 7 shows an overview of the evaluation method.

One end of the specimen 10 is supported by a rotatable support member 11, the other end is held by a holder 12 as shown in FIG. It is a reciprocating motion that makes a bend, and the span Q
The stress value of the test material is changed by adjusting the .

Fig. 2 shows fatigue strength evaluation using the above evaluation method.

From Figure 2, the corner radius dimensions are 0.08mm and 0.10
It can be seen that when the thickness is smaller than nm and 0.15 an, the fatigue strength is significantly inferior, and when it exceeds 0.611I11, the fatigue strength is saturated.

A test material having the chemical components shown in Table 3 was obtained.

Table 4 shows the properties of these test materials.

In Table 4, the degree of tension reduction is the load required to bend a 5φ x 150Q nine-piece to a radius of curvature of 25R at room temperature, and the load required to bend a 5φ x 150Q nine-piece to a radius of curvature of 25R at room temperature, and the load required to bend a 5φ x 150Q piece to a radius of curvature of 25R after heating at 300°C It shows the rate of decrease in the required load, and the lower the rate of decrease, the less the decrease in tension. In Table 4, the reduction rate of the cast iron ring is assumed to be 1, and the ratio of the reduction rate of each steel type to that is shown.

Table 4 shows that although the above material according to the present invention has excellent properties, when it is nitrided, the nitrogen concentration in the corner portion becomes high as described above, and that portion becomes brittle.

That is, the present invention can satisfy the characteristics required for a piston ring only by using a material having the above-mentioned composition and chamfering according to the present invention.

〔Effect of the invention〕

As described above, according to the present invention, the corner portion has a thickness of 0.15 to 0.
．． By chamfering 6 nn, it is possible to prevent breakage due to partial embrittlement of the corner portion after nitriding, thereby providing a nitrided piston ring, which is very useful industrially.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of a piston ring according to the present invention, Fig. 2 is an evaluation result of the present invention (relationship between corner radius and fatigue strength), and Figs. 3 to 5 are according to the present invention. A sectional view showing another embodiment, FIG. 6 is a sectional view of a sample material used in the evaluation of the present invention, FIG. 7 is a schematic diagram of the experimental equipment used in the evaluation of the present invention, and FIG. 8 is a conventional piston. FIG. 3 is a cross-sectional view of the ring. YO: Piston ring, 2: Top surface, 3: Bottom surface, 4: Inner peripheral surface, 5: Outer peripheral surface, 6: Nitrided layer, 7: Corner nitriding depth,
8: Nitriding depth other than corner parts, 9: Nitriding depth, 10:
Test material, 11: Support member, 12: Holder, 13: Test material installation state, a: Chamfer size on top or bottom side, b
: Chamfer dimensions on the inner or outer circumference side, Q = Nispan T
: Axial thickness, B: Axial width. Figure 1 Figure 3, Figure 4 Figure 5 Figure 6 Figure 2

Claims (1)

Claims: 1. A nitrided steel piston ring having a depth of 100 to 200 μm, in which the steel has a C0.
3 to 0.9%, Si 2.0% or less, Mn 2.0% or less,
Steel containing 2.0 to 9.0% Cr, and 0.15 to 0.60% in the piston ring cross-sectional corner part.
Steel piston ring characterized by chamfering in the mm range. 2 As a constituent element of steel, Al0.3-2.0%
A steel piston ring according to claim 1, which contains: 3 W, Mo, V and N as constituent elements of steel
Claim 1 containing one or more types of b.
The steel piston ring described in item 2 or item 2.